1. Field of the Invention
This invention relates to a novel catalyst system for the polymerization of alpha-olefins, process for producing this catalyst system, process for the stereoregular polymerization of alpha-olefins using such catalyst system, and a method of enhancing the stereospecificity of a catalyst system.
2. Prior Art
The polymerization of alpha-olefins in the presence of a catalyst system comprising (i) an organoaluminum containing component, and (ii) a titanium halide containing component is well known in the art and the polymers produced utilizing such catalyst systems have found numerous uses. The resulting crystalline polymers have associated therewith, to a greater or lesser degree, a low molecular weight amorphous polymer, which ranges from a viscous liquid to a soft tacky solid and is soluble in hydrocarbons, e.g. heptane. The production of a polymer having a low concentration of such amorphous polymer results in the polymer having highly desirable properties, such as hardness, density, tensile strength, melting temperature and molding and fiber forming properties. Thus, the production of highly stereoregular crystalline polymers having a low concentration of amorphous polymer is a desirable objective for a catalyst system and polymerization process.
It is also desirable that high amounts of polymer be produced per unit of time per unit of catalyst employed, i.e. the catalyst system should have a high activity. It is thus important that when seeking to improve the stereospecificity of a catalyst system, that the activity not be substantially decreased. Ideally, it is highly desirable to improve simultaneously the stereospecificity and activity of a catalyst system.
Various approaches to achieving the aforementioned objectives have been proposed in the art.
It is known in the art, for example, that activity and/or stereospecificity of a catalyst system containing an aluminum reduced titanium trichloride material may be enhanced by grinding the material.
It is also known that the activity and/or stereospecificity of Ziegler type catalysts can be modified by adding to the catalysts certain auxiliary components. For example, U.S. Pat. Nos. 3,701,763 and 3,850,899 to Wada et al. teach that stereoregular polymers can be provided if the titanium trichloride component is pulverized in the presence of auxiliary components, including certain aliphatic and aromatic ethers, amines and ketones. Such catalyst systems, generally still have a comparatively low activity and the polymer produced requires de-ashing.
Generally, these auxiliary components, e.g. electron donors, are used in the form of complexes, with the titanium compound, however, catalyst systems are known in which the electron donor can be used in combination with the organoaluminum compound in an amount as high as a 1:1 molar ratio of organoaluminum compound to electron donor.
Additionally, attempts to increase the activity of a catalyst system have been made by supporting the titanium halide compound on, for example, magnesium chloride.
When the polymerization of propylene is carried out with supported catalysts wherein the titanium compound is used in the form of a complex with an electron donor (such as a Lewis base) the stereospecificity of the catalyst is increased, but the amount of the amorphous polymer is still too high.
Attempts have also been made to improve the stereospecificity and/or activity of such catalyst systems by varying the amount of titanium compound to total electron donor compound present in the catalyst system, see for example, U.S. Pat. No. 4,107,414 to Giannini et al. These catalyst systems are still not completely satisfactory.